CN108051888B - Ring core optical fiber with concave refractive index - Google Patents
Ring core optical fiber with concave refractive index Download PDFInfo
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- CN108051888B CN108051888B CN201711428780.XA CN201711428780A CN108051888B CN 108051888 B CN108051888 B CN 108051888B CN 201711428780 A CN201711428780 A CN 201711428780A CN 108051888 B CN108051888 B CN 108051888B
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- core
- refractive index
- optical fiber
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- annular
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
- G02B6/0281—Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core
Abstract
The invention relates to a ring-core optical fiber with a depressed refractive index, wherein a ring-core fiber core of the ring-core optical fiber is depressed along the refractive index distribution from the outer side to the inner side. The ring-core optical fiber provided by the invention has a concave refractive index distribution design, can effectively inhibit the coupling and attenuation of a mode group in the transmission process, and can further increase the optical fiber transmission distance on the basis of not increasing the complexity of a system multi-input multi-output algorithm.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a ring-core optical fiber with a concave refractive index.
Background
With the development of the internet, the demand of people for communication capacity is continuously increasing. At present, due to the influence of the nonlinear effect of optical fibers and the spontaneous radiation noise of optical amplifiers, the capacity increase of commercial single-mode optical fiber communication systems has already met the bottleneck and cannot meet the rapid increase of the future communication capacity requirement. The mode division multiplexing optical fiber communication system based on few-mode optical fiber can break the nonlinear Shannon limit of single-mode optical fiber theoretically, has higher transmission capacity density, and has attracted wide attention in recent years. However, as the system capacity expands and the transmission distance increases, the complexity of the mimo algorithm in the mode division multiplexing system is also increasing to combat the mutual crosstalk between the modes and the inter-mode delay. Mode division multiplexing systems based on weakly coupled few-mode fibers have been proposed in recent years to reduce the complexity of the mimo algorithm. In these schemes, a multiple-input multiple-output algorithm is used to equalize inter-mode crosstalk within a mode group, and mode separation between mode groups can be achieved by a mode demultiplexer at a physical layer. However, as the order of the mode group is increased in the weakly coupled few-mode fiber, the number of modes in the mode group is increased, so that the complexity of a multiple-input multiple-output algorithm for equalizing crosstalk between modes in the mode group is increased, and further expansion of the system is limited.
The above problems are solved by the presence of an optical fiber having a ring-shaped core structure (ring-core fiber for short). Due to the radial constraint of the ring-core fiber, the radial order of the supported modes is unique, which means that the number of modes in the high-order mode group is always four. So that the complexity of the multiple-input multiple-output algorithm is not increased due to the increase of the order of the mode group. However, as the transmission distance of the optical fiber increases, crosstalk coupling between the ring core optical fiber mode groups increases. To avoid crosstalk coupling between mode groups, a multi-input multi-output algorithm is used for compensation, but the transmission distance of the ring-core fiber is limited.
Disclosure of Invention
The invention provides a ring-core optical fiber with a concave refractive index, aiming at solving the technical defect that the transmission distance of the ring-core optical fiber provided by the prior art is limited.
In order to achieve the purpose, the invention adopts the technical scheme that:
A ring-core optical fiber with a depressed refractive index is provided, wherein the refractive index distribution of the ring-core optical fiber along the outer side to the inner side direction is depressed.
In the scheme, the refractive index of the annular fiber core is higher than that of media on the inner side and the outer side of the annular fiber core, so that the radial order of the transmission mode in the fiber core is unique, the number of modes in the basic mode group is two, and the number of modes in each high-order mode group is four all the time. The crosstalk coupling between the mode groups in the ring core can be divided into adjacent-order mode crosstalk coupling and sub-adjacent-order mode crosstalk coupling. The principle of the ring-core optical fiber with the depressed refractive index distribution for inhibiting the crosstalk between modules is that the depressed refractive index distribution changes the radial distribution of the mode electric field in the ring-core. Compared with a common annular optical fiber, the electric field distribution in the annular thickness range of the annular core optical fiber with the concave refractive index distribution keeps consistent symmetry with the refractive index distribution, and the symmetry centers of the two distributions are closer, so that the module crosstalk coupling caused by perturbation is inhibited. The increased size of the index depression simultaneously suppresses crosstalk coupling between the adjacent and next adjacent steps and reduces loss. The increased depth of the index depression simultaneously suppresses crosstalk coupling between the adjacent and next adjacent steps and increases loss.
Preferably, the location where the refractive index profile is depressed is within the thickness of the annular core. .
Preferably, the inner diameter of the ring core is between 1 micron and 30 microns, and the thickness of the ring core is between 1 micron and 10 microns.
Preferably, the depth of the depression is between 1% and 70% of the maximum value of the difference between the annular core refractive index profile and the inner or outer refractive index; the depression width is 1% to 90% of the thickness of the annular core.
Preferably, the outer side of the annular core is provided with an annular low-refractive-index groove. The low-refractive-index groove serves to prevent mode leakage and improve energy transmission efficiency.
Preferably, the refractive index profile is graded.
Compared with the prior art, the invention has the advantages and beneficial effects that:
The ring-core optical fiber provided by the invention has a concave refractive index distribution design, can effectively inhibit the coupling and attenuation of a mode group in the transmission process, and can further increase the optical fiber transmission distance on the basis of not increasing the complexity of a system multi-input multi-output algorithm.
Drawings
Fig. 1 (a) is a cross-sectional view of an optical fiber.
FIG. 1 (b) is a refractive index profile of a cross-sectional diameter line of a ring core optical fiber.
FIG. 2 is a graph of the refractive index profile over the range of core thicknesses.
Detailed Description
In order to make the technical means, the creation features, the achievement purposes and the effects of the invention easy to understand, the following description further explains how the invention is implemented by combining the drawings and the specific embodiments.
FIG. 1 (a) is a cross-sectional view of an optical fiber, and FIG. 1 (b) is a refractive index profile at a diameter line of the cross-section, as shown in FIG. 1, the ring core optical fiber provided by the present invention has a concave refractive index profile, wherein the refractive index profile may be a graded-index profile, which may be represented by 5 or more segmented curves, each of which satisfies a formula of a graded-index curve, and the curves have smooth transitions therebetween. In fig. 1, the auxiliary line 1 identifies the outer boundary of the fiber cladding, 2 identifies the outer boundary of the fiber core, 3 identifies the center of symmetry of the refractive index profile of the fiber core within the ring width, and 4 identifies the inner boundary of the ring-shaped fiber core. (b) The core refractive index profile shown in (1) is embodied in a folded lug shape, and the depth of the recess accounts for 1 to 70 percent of the maximum value of the difference between the annular core refractive index profile and the inner side or outer side refractive index; the depression width is 1% to 90% of the thickness of the annular core.
FIG. 2 is a graph of the refractive index profile over the range of core thicknesses. The curve is divided into a plurality of sections of curves by the auxiliary lines. Wherein the auxiliary line 1 identifies an interface between the range of the thickness of the fiber core and the inner side of the ring or the outer side of the ring, the ranges identified by the auxiliary lines 1 and 2 are the rising edges of the refractive index distribution of the fiber core, the size of the rising edges accounts for 1 to 50 percent of the thickness of the fiber core, and the refractive index change value of the rising edges accounts for 30 to 99 percent of the total refractive index change value; the auxiliary lines 2 and 3 identify a first convex portion of the refractive index which receives the rising edge of the refractive index and the concave portion of the refractive index, the size of which is 1% to 50% of the thickness of the core, and the refractive index variation value of which is 1% to 70% of the total refractive index variation value; the auxiliary lines 3 and 4 identify depressed portions of the refractive index profile within the thickness of the core, the depressed portions having a size of 1% to 90% of the thickness of the core, and the depressed refractive index variation value of 1% to 70% of the total refractive index variation value; the auxiliary lines 4 and 5 identify a second convex portion of the refractive index, which receives the concave refractive index and the concave refractive index, whose size is 1% to 50% of the thickness of the core and whose refractive index variation value is 1% to 70% of the total refractive index variation value; the auxiliary lines 5 and 6 mark the falling edges of the refractive index, the size of the falling edges accounts for 1 to 50 percent of the thickness of the fiber core, and the refractive index change value of the falling edges accounts for 30 to 99 percent of the total refractive index change value; the auxiliary line 6 identifies the other interface of the core thickness range with the outside of the ring or the inside of the ring, and the auxiliary lines 1 and 6 identify the thickness range of the ring core. The curve shape has a large influence on the crosstalk coupling and loss of the mode groups in the core.
The crosstalk coupling between the mode groups in the ring core can be divided into adjacent-order mode crosstalk coupling and sub-adjacent-order mode crosstalk coupling. The principle of the depressed profile for suppressing inter-mode crosstalk is that the depression changes the radial distribution of the mode electric field in the ring core. Compared with the common annular optical fiber, the electric field distribution in the thickness range of the fiber core of the concave annular optical fiber keeps consistent symmetry with the refractive index distribution, and the symmetry centers of the two distributions are closer, so that the module crosstalk caused by the perturbation is inhibited. Specifically, the increase in the size of the refractive index depression suppresses crosstalk coupling between the adjacent step and the next adjacent step, and reduces loss; the increased depth of the index depression simultaneously suppresses crosstalk coupling between the adjacent and next adjacent steps and increases loss. It should be noted that having a depressed index profile describes the general shape of the index profile, including but not limited to the multi-segment curve segmentation of FIG. 2.
In this embodiment, an annular low refractive index groove is provided on the outer side of the annular core. The low-refractive-index groove serves to prevent mode leakage and improve energy transmission efficiency.
Finally, the above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent processes performed by the present invention or directly or indirectly applied to other related technical fields using the contents of the present specification and the attached drawings are included in the scope of the present invention.
Claims (5)
1. A depressed-index ring-core optical fiber, comprising: the refractive index distribution of the annular fiber core of the annular core fiber along the direction from the outer side to the inner side is provided with a recess;
the depth of the recess accounts for 1 to 70 percent of the maximum difference between the refractive index distribution of the annular fiber core and the refractive index at the inner side or the outer side; the depression width is 1% to 90% of the thickness of the annular core.
2. The depressed-index ring-core optical fiber of claim 1, wherein: the position where the refractive index profile is depressed is within the thickness of the annular core.
3. The depressed-index ring-core optical fiber of claim 1, wherein: the inner diameter of the annular core is between 1 micron and 30 microns, and the thickness of the annular core is between 1 micron and 10 microns.
4. The depressed-index ring-core optical fiber of claim 2, wherein: and an annular low-refractive-index groove is formed on the outer side of the annular fiber core.
5. The depressed-index ring-core optical fiber according to any one of claims 1 to 4, wherein: the refractive index distribution is a gradual change.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201711428780.XA CN108051888B (en) | 2017-12-26 | 2017-12-26 | Ring core optical fiber with concave refractive index |
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| CN201711428780.XA CN108051888B (en) | 2017-12-26 | 2017-12-26 | Ring core optical fiber with concave refractive index |
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| CN108051888A CN108051888A (en) | 2018-05-18 |
| CN108051888B true CN108051888B (en) | 2019-12-10 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| FR3087016A1 (en) * | 2018-10-08 | 2020-04-10 | Draka Comteq France | Low-mode, weakly coupled optical fibers for mode-division multiplexing and corresponding transmission system |
| CN109581680A (en) * | 2019-01-09 | 2019-04-05 | 邯郸学院 | Three rank linear polarization orbital angular momentum generator of all -fiber |
| CN109683234A (en) * | 2019-01-14 | 2019-04-26 | 北京交通大学 | A kind of weak mode-coupling resonat less fundamental mode optical fibre |
| CN110297288B (en) * | 2019-04-15 | 2020-12-29 | 长飞光纤光缆股份有限公司 | Low-attenuation step type track angular momentum optical fiber |
| CN110333572B (en) * | 2019-04-15 | 2020-11-24 | 长飞光纤光缆股份有限公司 | Low-attenuation graded orbital angular momentum optical fiber |
| CN112014921B (en) * | 2020-09-14 | 2021-06-11 | 东北大学 | Concave refractive index optical fiber for shaping Gaussian beam into flat-top beam |
| CN117420680B (en) * | 2023-12-18 | 2024-02-23 | 华中科技大学 | Photon lantern design method with mode-dependent loss equalization function |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CA2299576A1 (en) * | 1997-08-07 | 1999-02-18 | Corning Incorporated | Dispersion managed optical waveguide fiber |
| US6430347B1 (en) * | 1999-09-30 | 2002-08-06 | Corning Incorporated | Dispersion and dispersion slope compensated fiber link |
| US7668419B2 (en) * | 2006-10-23 | 2010-02-23 | Weatherford/Lamb, Inc. | Evanescent sensor using a hollow-core ring mode waveguide |
| DE102011109845B4 (en) * | 2010-11-04 | 2020-10-29 | J-Plasma Gmbh | Arrangement for the transmission of electromagnetic radiation, preferably for the application of light energy to biological structures and method for producing an optical waveguide for an arrangement |
| CN106707408A (en) * | 2017-03-28 | 2017-05-24 | 中山大学 | Graded index fiber based on ring-structure fiber core |
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